A large cap total market fund is a solid core holding. Keep in mind that some small cap stocks can do very well. So a total market fund (such as VTI) that includes small cap and mid cap stocks could give better performance.

Large cap stocks tend to be well established companies. They are often industry leaders and your funds should be safe there. But they also tend to be mature companies with little growth potential compared to the small caps which can be high risk but have large growth potential. Hence, a mix of the two can give better results over time.